Method of manufacturing electrocatalyst through one step electrodeposition and electrocatalyst manufactured therefrom

ABSTRACT

Disclosed is a method of manufacturing an electrocatalyst. The method may include forming a metal layer on a substrate, treating a substrate of the metal layer, and forming a catalyst layer on the metal layer by applying potential to an aqueous deposition solution including a nickel precursor, a copper precursor, a phosphorus precursor, and an additive, in which a molar ratio of the nickel precursor to the copper precursor may be greater than about 49:1. Accordingly, the present invention has an advantage in that the process of manufacturing the electrocatalyst may be simplified.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Korean PatentApplication No. 10-2018-0095514, filed on Aug. 16, 2018, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method of manufacturing anelectrocatalyst by electrodeposition.

BACKGROUND OF THE INVENTION

Since the current hydrogen energy has received attention as aneco-friendly energy capable of replacing fossil fuels and the hydrogenenergy can be produced only by electrolysis of water, interests instudies on an electrocatalyst that produces hydrogen energy byelectrolyzing water have been increased.

Typically, the electrocatalyst is composed of a hydrogen evolutionreaction (HER) electrode and an oxygen evolution reaction (OER)electrode. Platinum (Pt) has been the most widely known as a materialfor each electrode. However, since platinum corresponds to a noble metaland has a limitation on reserves, studies on using a metal rich inreserves, such as iron (Fe), nickel (Ni), copper (Cu), and cobalt (Co)as an element to replace platinum, particularly, studies on using aheterogeneous metal as a material for an electrocatalyst have beenactively conducted.

For instance, in the related arts, a cobalt phosphide doped with copperhas been used. However, a manufacturing process is complicated withbeing subjected to a carbonization process at 800° C. and a post-heattreatment process at 300° C. using a metal-organic framework (MOF) as aprecursor and only the activity in a strong base (pH 13.5) electrolytehas been reported.

In addition, in the related arts, a material in which a nickel (Ni) foamhas been doped with cobalt, which may involve a complicated process suchas formation of a layered nanostructure (three-layered morphology) onthe surface of the nickel foam using a sphere lithography process.Further, the material is amorphous and only the activity in a strongalkali (pH 13.5) electrolyte has been reported.

Moreover, in the related arts, a material has been prepared byelectrodepositing nickel and copper on a stainless steel foil, and thenapplying a phosphide treatment thereto (so-called a two-step process).However, the addition of phosphorus requires a process at 300° C., andthus is not efficient in terms of costs.

Despite in the related art has introduced using a nickel precursor, acopper precursor, and a phosphorus precursor that can beelectrodeposited, electrolyzing and removing liquid water or vapor watermolecules (moisture) may be limited because the invention exhibits superhydrophobicity and is used for surface waterproof treatment. Further,because additives for various purposes are used, such as the use of SDSand Na₂SO₄ as an ion strengthening agent and the use of aqueous ammoniaas a pH adjusting agent, the process may not be simplified.

SUMMARY OF THE INVENTION

In preferred aspect, the present invention may provide simplifiedprocess of process of manufacturing an electrocatalyst and reduce anadditive used in electrodeposition. In addition, the present inventionmay provide the process of manufacturing the electrocatalyst to removemoisture.

In an aspect, provided is a method of manufacturing an electrocatalyst.The method may include forming a metal layer on a substrate, treating asurface of the metal layer, and forming a catalyst layer on the metallayer by applying potential to an aqueous deposition solution includinga nickel precursor, a copper precursor, a phosphorus precursor, and anadditive. In particular, a molar ratio of the nickel precursor to thecopper precursor may be greater than about 49:1 to 499:1, or morepreferably between about 99:1 to about 499:1.

The “aqueous deposition solution” is meant by an admixture or a solutionincluding water or water-based solvent for dispersing of other materialsor components.

The metal layer may suitably include a nickel layer or a copper layer.

The treating the surface of the metal layer. Preferably, the treatingmay provide the hydrophilic surface, for example, the hydrophilicsurface treatment may suitably include a UV-ozone cleaning treatment.

The potential may be applied by a cyclic voltammetry method.

Preferably, a range of the potential may be about −1.2 to 0.2 V,including from about −1.0 V to 0.2 V, −0.8 V to 0.2 V or −0.6 V to 0.2V.

A frequency at which the range of the potential is applied may suitablybe about 3 to 15 times.

A molar concentration of the nickel precursor may be of about 0.02 to0.5 M, including 0.05 to 0.2 M or 0.1 to 0.15 M.

The nickel precursor may suitably include one or more selected fromnickel sulfate, nickel nitrate, and nickel acetate.

A concentration of the copper precursor may be of about 0.001 to 0.02 M.

The copper precursor may suitably include one or more selected fromcopper sulfate, copper nitrate, copper acetate, and copperacetylacetonate.

The additive may suitably include sodium acetate, and may furtherinclude glycine or citric acid.

A molar ratio of the nickel precursor to sodium acetate, glycine, orcitric acid may be about 1:about 0.5 or greater and about 1:less thanabout 2.

A molar concentration of each of sodium acetate, glycine, and citricacid may be of about 0.05 or greater and less than about 0.2 M.

A molar ratio of the nickel precursor to the phosphorus precursor may beof about 1:about 5 to about 1:about 20, more preferably, of about1:about 5 to about 1:about 10.

A molar concentration of the phosphorus precursor may be of about 0.01 Mto about 2.0 M, about 0.05 to about 1.5 M, or more preferably, of about0.1 to 1.25 M.

The phosphorus precursor may suitably include sodium hypophosphite.

A substrate on which the nickel copper-phosphide catalyst layer isdeposited may be pretreated. The pre-treatment may be an oxygen plasmaetching process.

In another aspect, provided is an electrocatalyst including an oxygengeneration electrode and a hydrogen generation electrode which may bemanufactured by the method descried herein. At least one of theelectrodes may include a substrate and a catalyst layer electrodepositedonto the substrate, and the catalyst layer may include greater thanabout 65 at % of nickel; and less than about 35 at % of copper, based on100 at % of metal atoms. In preferred aspect, the catalyst layer mayinclude Ni greater than about 66, 70, 75, 80, 85, 90, or 95 at % andinclude Cu less than about 34, 30, 25, 20, 15, 10 or 5 at %, based on100 at % of total metal atom. In all the catalyst layer will containcopper, i.e. the amount of copper will be greater than 0 at % orpreferably will be at least about 0.5 wt % or greater based on 100 at %of metal atoms.

The electrocatalyst may include a metal layer between the substrate andthe catalyst layer. The metal layer may suitably include a nickel layeror a copper layer.

According to the various exemplary embodiments, the present inventionmay provide a simplified process of manufacturing an electrocatalyst andan additive used during an electrodeposition. Further, the methoddisclosed herein may remove moisture.

Still further provided is a vehicle part that may include theelectrocatalyst as described herein. Exemplary vehicle part may includea headlamp. Also provided is a vehicle including the vehicle part asdisclosed herein.

Other aspects of the invention are disclosed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart of an exemplary process for manufacturing anexemplary electrocatalyst by a single-step electrodeposition accordingto an exemplary embodiment of the present invention.

FIG. 2 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5M)according to the thickness of a nickel layer when the nickel layer isformed on a conductive substrate.

FIG. 3 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5M)according to the circulation frequency when the range of the potentialand the scan rate are −1.2 to 0.2 V and 10 mV/s, respectively.

FIG. 4 is a graph showing a ratio (at %) of nickel and copper atoms inan exemplary catalyst layer according to the molar ratio of the nickelprecursor to the copper precursor in an exemplary embodiment of thepresent invention.

FIG. 5 is a linear sweep voltammetry (LSV) graph according to the ratio(at %) of nickel and copper atoms.

FIG. 6A illustrates XRD patterns and crystal analyses according to theratio (at %) of nickel and copper atoms in an exemplary embodiment ofthe present invention, and FIG. 6B enlarges XRD patterns at about 43° toabout 45.5° among the diffraction angles in FIG. 6A. FIG. 6C enlargesXRD patterns of Ni₈₉Cu₁₁—P illustrated in FIG. 6A.

FIG. 7A is a transmission electron microscope (TEM) image of a portionin which Ni-rich nickel copper-phosphide in an exemplary Ni₆₅Cu₃₅—Pcatalyst layer appears in an exemplary embodiment of the presentinvention, and FIG. 7B is a fast Fourier transformed image of FIG. 7A.

FIG. 8A is a transmission electron microscope image of a portion inwhich Cu-rich nickel copper-phosphide in an exemplary Ni₆₅Cu₃₅—Pcatalyst layer appears in an exemplary embodiment of the presentinvention, and FIG. 8B is a fast Fourier transformed image of FIG. 8A.

FIG. 9A is a transmission electron microscope image of a portion inwhich Ni₁₂P₅ crystals in an exemplary Ni₆₅Cu₃₅—P catalyst layer appearin an exemplary embodiment of the present invention, and FIG. 9B is afast Fourier transformed image of FIG. 9A.

FIG. 10A is a transmission electron microscope image of a portion inwhich Ni₃P crystals in an exemplary Ni₆₅Cu₃₅—P catalyst layer appear inan exemplary embodiment of the present invention, and FIG. 10B is a fastFourier transformed image of FIG. 10A.

FIG. 11 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the concentration of sodium acetate when the concentrationof the nickel precursor is 0.1 M.

FIG. 12 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the concentration of glycine when the concentration of thenickel precursor is 0.1 M.

FIG. 13 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the concentration of citric acid when the concentration ofthe nickel precursor is 0.1 M.

FIG. 14 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the molar ratio of the nickel precursor to the phosphorusprecursor.

FIG. 15A is an image captured by a scanning electron microscope (SEM)after 10 V is applied to a pretreated OER electrode for 10 minutes, andFIGS. 15B, 15C and 15D are images captured by enlarging the image inFIG. 15A.

FIG. 16A is an image captured by a scanning electron microscope after 10V is applied to a non-pretreated OER electrode for 10 minutes, and FIGS.16B, 16C and 16D are images captured by enlarging the image in FIG. 16A.

FIG. 17 is a graph comparing the conductivity of an exemplary Ni₉₁Cu₉—Pelectrocatalyst with that of a Ni—P electrocatalyst in an exemplaryembodiment of the present invention.

FIG. 18 is a graph comparing the charge mobility of an exemplaryNi₉₁Cu₉—P electrocatalyst with that of a Ni—P electrocatalyst in anexemplary embodiment of the present invention.

FIG. 19 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)of an exemplary Ni₉₁Cu₉—P electrocatalyst in an exemplary embodiment ofthe present invention, a Pt electrocatalyst, a Ni—P electrocatalyst, aNiCu electrocatalyst, a Ni electrocatalyst, and a Cu electrocatalyst.

FIG. 20 is a graph measuring a hydrogen evolution reaction (KOH 1 M) ofan exemplary Ni₉₁Cu₉—P electrocatalyst in an exemplary embodiment of thepresent invention, a Pt electrocatalyst, a Ni—P electrocatalyst, a NiCuelectrocatalyst, a Ni electrocatalyst, and a Cu electrocatalyst.

FIGS. 21A-21B are scanning electron microscope images when a potentialof 10 V is applied to an exemplary HER electrode of an exemplaryNi₉₁Cu₉—P electrocatalyst for 10 minutes in an exemplary embodiment ofthe present invention.

FIGS. 22A-22B are scanning electron microscope images when a potentialof 10 V is applied to an exemplary OER electrode of an exemplaryNi₉₁Cu₉—P electrocatalyst for 10 minutes in an exemplary embodiment ofthe present invention.

FIG. 23 illustrates a current density according to the potential appliedto an exemplary Ni₉₁Cu₉—P electrocatalyst in an exemplary embodiment ofthe present invention.

FIG. 24A illustrates an exemplary Ni₉₁Cu₉—P electrocatalyst in anexemplary embodiment of the present invention mounted in a headlamp andmoisture, and FIG. 24B illustrates a region in which moisture around theNi₉₁Cu₉—P electrocatalyst is removed.

FIG. 25 is a graph measuring the current density according to thehumidity of an exemplary Ni₉₁Cu₉—P electrocatalyst in an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION

Hereinafter, the present invention will be described in detail. However,the present invention is not limited or restricted by exemplaryembodiments, objects and effects of the present invention will benaturally understood or become apparent from the following description,and the objects and effects of the present invention are not limited byonly the following description. Further, in the description of thepresent invention, when it is determined that the detailed descriptionfor the publicly-known technology related to the present invention canunnecessarily obscure the gist of the present invention, the detaileddescription thereof will be omitted.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise. It willbe further understood that the terms “comprise”, “include”, “have”, etc.when used in this specification, specify the presence of statedfeatures, regions, integers, steps, operations, elements and/orcomponents but do not preclude the presence or addition of one or moreother features, regions, integers, steps, operations, elements,components, and/or combinations thereof.

It is understood that the term “vehicle” or “vehicular” or other similarterm as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g. fuels derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example bothgasoline-powered and electric-powered vehicles.

Further, unless specifically stated or obvious from context, as usedherein, the term “about” is understood as within a range of normaltolerance in the art, for example within 2 standard deviations of themean. “About” can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%,3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unlessotherwise clear from the context, all numerical values provided hereinare modified by the term “about.”

FIG. 1 is a flowchart of the present invention which manufactures anexemplary electrocatalyst by a single-step electrodeposition in anexemplary embodiment of the present invention. As shown in FIG. 1, thepresent invention may include forming a metal layer on a substrate(S101), treating the surface of the metal layer, for example,hydrophilic surface treatment (S102), and forming a catalyst layer,e.g., nickel copper-phosphide catalyst layer, on the metal layer byapplying potential to an aqueous deposition solution including a nickelprecursor, a copper precursor, a phosphorus precursor, and an additive(S103).

The single-step electrodeposition may suitably include forming a nickelcopper-phosphide catalyst layer with single electrodeposition, and thenickel copper-phosphide catalyst layer may suitably include a catalystlayer having a crystal structure in which phosphorus may be depositedinto an interstitial site of nickel and copper ions may be deposited bysubstituting nickel atoms located in the nickel interstices with copperions.

As the substrate, a glass or silicon wafer may suitably be used, and ametal layer formed on the substrate may suitably include a nickel layeror a copper layer. Moreover, the metal layer may be formed by sputteringor electron beam. However, the deposition method may not be limitedthereto as long as the deposition method does not affect theelectrodeposition of an aqueous deposition solution.

FIG. 2 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the thickness of a nickel layer when the nickel layer isformed on a conductive substrate. As shown in FIG. 2, the nickel layermay suitably have a thickness of about 50 to 300 nm. Since a metal layersuch as a nickel layer serves as a channel to transfer electric chargesduring an electrodeposition, the thickness thereof is not necessarilylimited to 50 to 300 nm.

The treating of the metal layer such as hydrophilic surface treatmentmay be a UV-ozone cleaning treatment. The hydrophilic surface treatmentmay increase the bonding strength between the surface of a substrate andan aqueous deposition solution including a precursor by surfacemodification, for example, forming a hydroxyl group (—OH). In addition,the hydrophilic surface treatment may prevent bubbles from beinggenerated on the surface of the substrate during the electrodeposition.However, the hydrophilic surface treatment is not limited thereto, and asurface treatment using plasma and the like may suitably be used.

When a nickel copper-phosphide catalyst layer is formed, the potentialmay be applied by a cyclic voltammetry method. The potential applied maybe set as to be less than reduction potentials of nickel, copper, andphosphorus (e.g., +0.272 V, +0.859 V, and 0.348 V, respectively vsAg/AgCl), and preferably, the range of the potential may be about −1.2to 0.2 V.

The frequency (circulation frequency) at which about −1.2 to 0.2 V isapplied may be about 3 to 15 times. When the circulation frequency isless than 3 times, the nucleation followed by the growth of the ioncatalyst layer may not uniformly occur over the entire region of themetal layer, and when the circulation frequency is greater than 15times, catalyst characteristics may deteriorate.

FIG. 3 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the circulation frequency when the range of the potentialand the scan rate are −1.2 to 0.2 V and 10 mV/s, respectively. As shownin FIG. 3, the hydrogen generation effects of electrocatalystsmanufactured by setting the circulation frequency to 3 times to 15 timesmay be better than those of electrocatalysts manufactured by setting thecirculation frequency to 1 time, 2 times, and 20 times.

When the circulation frequency is set to 3 times to 15 times, thecatalyst layer may be formed uniformly over the entire region of themetal layer, and catalyst characteristics may not deteriorate. However,the nickel copper-phosphide catalyst layer may also be formed by using aconstant current method (10 to 20 mA/cm²) instead of a cyclicvoltammetry method.

The molar ratio of the nickel precursor to the copper precursor includedin the aqueous deposition solution of the present invention may begreater than about 49:1. The molar ratio will be described below indetail.

FIG. 4 is a graph showing a ratio (at %) of nickel and copper atoms inthe catalyst layer according to the molar ratio of the nickel precursorto the copper precursor, and FIG. 5 is a linear sweep voltammetry graphaccording to the ratio (at %) of nickel and copper atoms. Tables 1 and 2show the results of measuring the ratio of nickel and copper atoms inthe catalyst layer according to the molar ratio of nickel and copperprecursors by EDX, and over voltages at 10 mA/cm² when each catalystlayer is used as a catalyst layer of a hydrogen generation electrode,respectively.

TABLE 1 Molar ratio of nickel and copper precursors 100:0 499:1 199:199:1 49:1 Composition of catalyst layer Ni—P Ni₉₃Cu₇—P Ni₉₁Cu₉—PNi₈₉Cu₁₁—P Ni₆₅Cu₃₅—P Overvoltage −82 −69 −48 −66 −126 (mV)

TABLE 2 Molar ratio of nickel and copper precursors 24:1 10.1:1 0:100Composition of catalyst layer Ni₃₆Cu₆₄—P Ni₂₃Cu₇₇—P Cu—P Overvoltage−259 −247 −359 (mV)

As shown in FIGS. 4 and 5 and Tables 1 and 2, the nickel precursor andthe copper precursor may suitably be included at a molar ratio of about199:1 in the aqueous deposition solution, and when the nickelcopper-phosphide catalyst layer is composed of about 91 at % of nickeland about 9 at % of copper based on 100 at % of metal atoms, that is,the Ni₉₁Cu₉—P catalyst layer is used as a catalyst layer of a hydrogengeneration electrode, the overvoltage measured at a current density of10 mA/cm² is −48 mV, which is the lowest value.

The over voltages measured from the Ni₉₃Cu₇—P catalyst layer, theNi₉₁Cu₉—P catalyst layer or the Ni₈₉Cu₁₁—P catalyst layer formed formaqueous deposition solutions in which the molar ratio of the nickelprecursor to the copper precursor was 499:1, 199:1, or 99:1 were lowerthan the overvoltage measured from the Ni—P catalyst layer formed fromthe aqueous deposition solution including no copper precursor.

These results are shown because electric charges accumulated betweennickel and phosphorus are decreased by doping the nickel-phosphoruscatalyst layer with copper. In other words, free electrons may beincreased, and the hydrogen adsorption energy may converge to 0.

Meanwhile, when the molar ratio of the nickel precursor to the copperprecursor in the aqueous deposition solution is equal to or less thanabout 49:1, that is, the ratio of copper atoms is about 35 at % orgreater, catalyst characteristics rapidly may deteriorate. For example,because a nickel copper-phosphide layer with a uniform composition isnot formed as the copper-phosphide is first deposited onto the metallayer as described below, the phase separation occurs.

Accordingly, the nickel precursor and the copper precursor may beincluded at a ratio greater than a molar ratio of the nickel precursorand the copper precursor included in the aqueous deposition solution ofthe present invention of about 49:1 where catalyst characteristicsrapidly deteriorate.

FIG. 6A illustrates XRD patterns and crystal analyses according to theratio (at %) of nickel and copper atoms, and FIG. 6B enlarges XRDpatterns at about 43° to about 45.5° among the diffraction angles inFIG. 6A. FIG. 6C enlarges XRD patterns of the Ni₈₉Cu₁₁—P catalyst layerillustrated in FIG. 6A. Table 3 shows the crystals where the peaksappear and the positions of the peaks.

TABLE 3 Cu (200) Ni (200) Cu (111) Ni (111) Peak angle 43.63° 44.66°50.95° 51.98°

As shown in FIGS. 6A to 6C and Table 3, when the catalyst layer includes7 at % or greater of copper atoms, peaks appear at 44.66° and 51.98°,corresponding to a Ni (200) surface and a Ni (111) surface, andaccordingly, the nickel copper-phosphide catalyst layer may be formed bythe analysis of XRD patterns.

In the Ni₈₉Cu₁₁—P catalyst layer, peaks appeared at 44.66° and 51.98°,whereas peaks appeared very finely at 43.63° and 50.95° corresponding tothe Cu (200) surface and the Cu (111) surface. For instance, as thecopper-phosphide was first deposited onto the metal layer, the phaseseparation finely occurred with a copper-phosphide and anickel-phosphide. However, since the Ni₈₉Cu₁₁—P catalyst layer exhibitsan overvoltage lower than those of the Ni—P catalyst layer and theNi₉₃Cu₇—P catalyst layer, the effect of increasing the electricconductivity according to the addition (doping) of copper moresignificantly may act than the effect caused by the formation of anon-uniform catalyst layer.

In the Ni₆₅Cu₃₅—P catalyst layer, the Ni₃₆Cu₆₄—P catalyst layer, and theNi₂₃Cu₇₇—P catalyst layer, which had a copper atom ratio greater thanabout 11 at %, peaks clearly appeared at 43.63° and 50.95°. As a copperprecursor at high concentration is included in the aqueous depositionsolution, the phase separation of the copper phosphide remarkablyappears. Since catalyst characteristics (overvoltage) of each catalystlayer rapidly deteriorate, the nickel precursor and the copper precursormay not be included at a copper atom ratio greater than a copper atomratio of about 35 at % or at a molar ratio of the nickel precursor tothe copper precursor in the aqueous deposition solution, which may beequal to or less than about 49:1. Hereinafter, the phase separation inthe Ni₆₅Cu₃₅—P catalyst layer will be described in detail.

FIG. 7A is a transmission electron microscope image of a portion inwhich Ni-rich nickel copper-phosphide in a Ni₆₅Cu₃₅—P catalyst layerappears, and FIG. 7B is a fast Fourier transformed image of FIG. 7(A).As shown in FIG. 7A and FIG. 7B, Ni-rich nickel copper-phosphide may beformed in the Ni₆₅Cu₃₅—P catalyst layer because the inverse number ofthe length of each of an arrow mark indicating a direction of about 8o'clock and an arrow mark indicating a direction between about 4 o'clockand about 5 o'clock is the same as the (200) surface and the (111)surface corresponding to the crystal surface of the Ni-rich nickelcopper-phosphide.

FIG. 8A is a transmission electron microscope image of a portion inwhich Cu-rich nickel copper-phosphide in a Ni₆₅Cu₃₅—P catalyst layerappears, and FIG. 8B is a fast Fourier transformed image of FIG. 8A. Asshown in FIGS. 8(A) and 8(B), Cu-rich nickel copper-phosphide may beformed in the Ni₆₅Cu₃₅—P catalyst layer because the inverse number ofthe length of each of an arrow mark indicating a direction of about 6o'clock and an arrow mark indicating a direction between about 2 o'clockand about 3 o'clock is the same as the (100) surface and the (200)surface corresponding to the crystal surface of the Cu-rich nickelcopper-phosphide.

FIG. 9A is a transmission electron microscope image of a portion inwhich Ni₁₂P₅ crystals in a Ni₆₅Cu₃₅—P catalyst layer appear, and FIG. 9Bis a fast Fourier transformed image of FIG. 9A. As shown in FIGS. 9S-9B,Ni₁₂P₅ crystals are formed in the Ni₆₅Cu₃₅—P catalyst layer because theinverse number of the length of each of an arrow mark indicating adirection of about 1 o'clock and an arrow mark indicating a directionbetween about 7 o'clock and about 8 o'clock is the same as the (420)surface and the (321) surface corresponding to the Ni₁₂P₅ crystalsurface.

FIG. 10A is a transmission electron microscope image of a portion inwhich Ni₃P crystals in a Ni₆₅Cu₃₅—P catalyst layer appear, and FIG. 10Bis a fast Fourier transformed image of FIG. A. As shown in FIGS.10A-10B, Ni₃P crystals may be formed in the Ni₆₅Cu₃₅—P catalyst layerbecause the inverse number of the length of each of an arrow markindicating a direction of about 1 o'clock and an arrow mark indicating adirection of about 7 o'clock is the same as the (330) surface and the(321) surface corresponding to the Ni₃P crystal surface.

Meanwhile, the molar concentration of the nickel precursor may be about0.02 to 0.5 M, and the nickel precursor may be at least one or more ofnickel sulfate, nickel nitrate, or nickel acetate.

The concentration of the copper precursor may be about 0.001 to 0.02 M,and the copper precursor may suitably include one or more selected fromcopper sulfate, copper nitrate, copper acetate, and copperacetylacetonate.

The additive included in the aqueous deposition solution of the presentinvention includes sodium acetate, and may further include glycine orcitric acid. Sodium acetate as used herein may regulate the reductionrate of metal ions by maintaining the pH and regulating the depositionreaction, and glycine and citric acid may be a so-called complexingagent which may inhibit metal ions from being bonded to oxygen,hydrogen, and the like which may be easily bonded and promotes thebonding of metal ions to phosphorus (P).

A molar ratio of the nickel precursor included in the aqueous depositionsolution of the present invention to sodium acetate, glycine, or citricacid may be about 1:about 0.5 or greater and about 1:less than about 2.When the molar ratio is about 1:about 2 or greater, the bonding strengthbetween the metal ions and the additive may be increased, so thatuniform electrodeposition may not be achieved. Accordingly, catalystcharacteristics may deteriorate.

FIG. 11 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the concentration of sodium acetate when the concentrationof the nickel precursor is 0.1 M, FIG. 12 is a graph measuring ahydrogen evolution reaction (H₂SO₄ 0.5 M) according to the concentrationof glycine when the concentration of the nickel precursor is 0.1 M, andFIG. 13 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the concentration of citric acid when the concentration ofthe nickel precursor is 0.1 M.

As shown in FIGS. 11 to 13, when the molar ratio of the nickel precursorto sodium acetate, glycine, or citric acid is about 1:0.5 and 1:1, theexcellent hydrogen generation effect may be exhibited, but when themolar ratio is about 1:2, the hydrogen generation effect deteriorates.

Meanwhile, a molar concentration of each of sodium acetate, glycine, andcitric acid may be about 0.05 to 0.1 M, and glycine or citric acid maybe suitably used. However, glycine and citric acid may be used inmixture as long as the bonding and reaction between glycine and citricacid may not affect the role of the complexing agent.

The aqueous deposition solution of the present invention may be anaqueous solution with a molar ratio of the nickel precursor to thephosphorus precursor of about 1:about 5 or greater and about 1:less thanabout 20. When the molar ratio is 1:5 or greater, electrodeposition maybe achieved without an ion strengthening agent (for example, SDS,Na₂SO₄, and the like) and a pH adjusting agent (for example, aqueousammonia) used for the electrodeposition, and when the molar ratio is1:20 or greater, characteristics of the electrocatalyst may deteriorate.

FIG. 14 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)according to the molar ratio of the nickel precursor to the phosphorusprecursor, and Table 4 shows over voltages measured at 10 mA/cm² whenthe molar ratio of the nickel precursor to the phosphorus precursor isvaried.

TABLE 4 Molar ratio of nickel and phosphorus precursors 1:2 1:5 1:101:20 Overvoltage −85 −82 −74 −84 (mV)

As shown in FIG. 14 and Table 4, when the molar ratio of the nickelprecursor to the phosphorus precursor is 1:5 and 1:10, the hydrogengeneration effect may be substantially improved, whereas when the molarratio of the precursors is 1:2 or 1:20, the hydrogen generation effectmay deteriorate. Meanwhile, the molar concentration of the phosphorusprecursor may be about 0.1 to 1.25 M, and the phosphorus precursor maybe sodium hypophosphite.

A substrate onto which the nickel copper-phosphide catalyst layer isdeposited may be pretreated, for example, a substrate to be used as anOER electrode may be pretreated. When an electrocatalyst is etched athigh potential, the electrocatalyst may be damaged due to the sharpincrease of current, so that the electrocatalyst may be pretreated inorder to improve the durability of the electrocatalyst. The pretreatmentmay be an oxygen plasma etching process, but is not limited thereto.

FIG. 15A is an image captured by a scanning electron microscope after 10V is applied to a pretreated OER electrode for 10 minutes, and FIGS. 15Bto 15D are images captured by enlarging the image in FIG. 15A. As shownin FIGS. 15A-15D, catalytic reactions were observed at the centrallongitudinal axis and the central horizontal axis in FIGS. 15A and 15B,but no desiccation crack was observed.

FIG. 16A is an image captured by a scanning electron microscope after 10V is applied to a non-pretreated OER electrode for 10 minutes, and FIGS.16B-16D are images captured by enlarging the image in FIG. 16A. As shownin FIGS. 16A-16D, a plurality of desiccation cracks was observed.

Thus, the durability of the electrocatalyst including the nickel-copperphosphide catalyst layer may be increased as a pretreatment, forexample, an oxygen plasma etching is performed, and the durabilityagainst a potential of 10 V may be obtained.

Example

Hereinafter, a process of manufacturing a Ni₉₁Cu₉—P catalyst layer asthe Example of the present invention will be described in detail.However, the Examples described below are only provided for specificallyexemplifying or explaining the present invention, and the presentinvention is not limited thereby.

A nickel layer was formed to have a thickness of 50 nm on a siliconwafer by using an electron beam deposition apparatus, and the substratewas subjected to hydrophilic surface treatment with a UV ozone cleaner(AC-6, 15 to 20 mW/cm²) for 10 minutes.

An aqueous deposition solution was prepared by mixing nickel sulfate,copper sulfate, and sodium hypophosphite, which are a nickel precursor,a copper precursor, and a phosphorus precursor, respectively, and sodiumacetate and citric acid, which are additives with distilled water. Themolar ratio of the nickel precursor to the copper precursor was adjustedto 199:1, the molar ratio of the nickel precursor to each additive wasadjusted to 1:1, and the molar ratio of the nickel precursor to thephosphorus precursor was adjusted to 1:10.

After the aqueous deposition solution was purged with a nitrogen gas for20 minutes, a Ni₉₁Cu₉—P catalyst layer was formed by using anelectroplating apparatus. In the formation of the catalyst layer, athree-electrode (counter electrode: graphite rod, reference electrode:Ag/AgCl) cyclic voltammetry method was used. The range of potential tobe applied was −1.2 to 0.2 V, the cyclic frequency was set to threetimes, and the scan rate was set to 10 mV/s.

A substrate on which the catalyst layer was formed afterelectrodeposition was washed with ethanol and distilled water in thisorder, and then dried at room temperature. Among the manufacturedsubstrates, a substrate to be used as an OER electrode was oxygen plasmaetched under the conditions of 100 W, 20 Pa, and 100 sccm of O₂ for 30minutes by using a reactive ion etcher (RIE) apparatus.

A Ni₉₁Cu₉—P electrocatalyst to be mentioned below refers to anelectrocatalyst in which a Ni₉₁Cu₉—P catalyst layer manufacturedaccording to the aforementioned Example is used as a catalyst layer of aHER electrode and/or an OER electrode of the electrocatalyst.

FIGS. 17 and 18 are graphs comparing the conductivity and chargemobility of a Ni₉₁Cu₉—P electrocatalyst with those of a Ni—Pelectrocatalyst. As shown in FIGS. 17 and 18, the Ni₉₁Cu₉—Pelectrocatalyst had greater conductivity over the entire regions ofpotential than that of the Ni—P electrocatalyst, and the Ni₉₁Cu₉—Pelectrocatalyst had low resistance because the Ni₉₁Cu₉—P electrocatalystdraws a circle with a relatively smaller diameter toward the x-axis thanthe Ni—P electrocatalyst.

FIG. 19 is a graph measuring a hydrogen evolution reaction (H₂SO₄ 0.5 M)of a Ni₉₁Cu₉—P electrocatalyst, a Pt electrocatalyst, a Ni—Pelectrocatalyst, a NiCu electrocatalyst, a Ni electrocatalyst, and a Cuelectrocatalyst. Table 5 shows over voltages measured when the currentdensity of each electrocatalyst is 10 mA/cm².

TABLE 5 Composition of electrocatalyst Ni₉₁Cu₉—P Pt Ni—P NiCu Ni CuOvervoltage (mV) −48 −129 −82 −406 −338 −439

As shown in FIG. 19 and Table 5, the Ni₉₁Cu₉—P electrocatalyst had anovervoltage measured at a lower level than the overvoltage of a Ptelectrocatalyst, which may be a representative electrocatalyst, and hadan overvoltage measured at a lower level than the overvoltage of theNi—P electrocatalyst. Through FIG. 19 and Table 5, the Ni₉₁Cu₉—Pelectrocatalyst had an excellent effect in the hydrogen evolutionreaction.

FIG. 20 is a graph measuring an oxygen evolution reaction (KOH 1 M) of aNi₉₁Cu₉—P electrocatalyst, a Pt electrocatalyst, a Ni—P electrocatalyst,a NiCu electrocatalyst, a Ni electrocatalyst, and a Cu electrocatalyst.Table 6 shows over voltages measured when the current density of eachelectrocatalyst is 10 mA/cm².

TABLE 6 Composition of electrocatalyst Ni₉₁Cu₉—P Pt Ni—P NiCu Ni CuOvervoltage (mV) 290 >1,000 450 650 590 620

As shown in FIG. 20 and Table 6, the Ni₉₁Cu₉—P electrocatalyst also hadan overvoltage measured at a lower level in the oxygen evolutionreaction than the overvoltage of a Pt electrocatalyst, and had anovervoltage measured at a lower level than the overvoltage of the Ni—Pelectrocatalyst. Through FIG. 20 and Table 6, the Ni₉₁Cu₉—Pelectrocatalyst also had an excellent effect in the oxygen evolutionreaction.

FIGS. 21A-21B and 22A-22B are scanning electron microscope images when apotential of 10 V is applied to a HER electrode and an OER electrode ofa Ni₉₁Cu₉—P electrocatalyst for 10 minutes. As shown in FIGS. 21A-21Band 22A-22B, the HER electrode and the OER electrode may be durable athigh potential because no desiccation crack was observed on the surfaceof the HER electrode and the surface of the OER electrode.

FIG. 23 illustrates a current density according to the potential appliedto a Ni₉₁Cu₉—P electrocatalyst. Table 7 shows the current density whenthe potential is 2 V, 5 V, 7 V, and 10 V.

TABLE 7 Potential (V) 2 5 7 10 Current density 0.31 0.88 1.33 2.06(mA/cm²)

As shown in FIG. 23 and Table 7, because the Ni₉₁Cu₉P-electrocatalystexhibited a predetermined current density at a potential of 10 V orless, the electrocatalyst was stably operated even though high potentialwas applied to the electrocatalyst.

FIG. 24A illustrates a Ni₉₁Cu₉—P electrocatalyst 10 mounted in aheadlamp, and FIG. 24B illustrates a region 11 in which moisture aroundthe Ni₉₁Cu₉—P electrocatalyst is removed. As shown in FIGS. 24A-24B, theNi₉₁Cu₉—P electrocatalyst 10 may be mounted at a lower portion of theinner side surface of a headlamp lens, preferably at a lower end portionof the inner side surface of the lens. Since moisture may remain at theend portion of the headlamp when the lamp is lit, the electrocatalystmay be mounted at a lower portion of the inner side surface of theheadlamp lens because moisture produced on the surface of theelectrocatalyst device can be removed, and water drops flowing down atthe inner side surface of the lens can be broken down. However, theposition of the electrocatalyst is not limited as long as the operationof the headlamp and the driver's view are not obstructed.

FIG. 25 is a graph measuring the current density according to thehumidity of the Ni₉₁Cu₉—P electrocatalyst. Table 8 shows the currentdensity when a potential of 10 V is applied and the humidity is 20%,70%, 90%, and 99%.

TABLE 8 Humidity (%) 20 70 90 99 Current density 0.06 0.3 0.6 1.08(mA/cm²)

As shown in FIG. 25 and Table 8, as the humidity is increased, thecurrent density may be increased, and the current density at eachhumidity may be constantly shown. Moreover, the ability to removemoisture may be constantly maintained while the Ni₉₁Cu₉—Pelectrocatalyst is stably operated at a potential of 10 V. Meanwhile, inthe Ni₉₁Cu₉—P electrocatalyst, 0.1 μl of water per hour was removed at ahumidity of 99%.

The present invention has been described in detail throughrepresentative Examples, but it is to be understood by a person withordinary skill in the art to which the present invention pertains thatvarious modifications are possible in the above-described Exampleswithin the range not departing from the scope of the present invention.Therefore, the scope of the present invention should not be limited tothe above-described Examples but should be determined by not only theclaims to be described below but also all the changes or modified formsderived from the claims and the equivalent concept thereof.

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

-   -   10: Ni₉₁Cu₉—P Electrocatalyst    -   11: Region in which moisture is remove

What is claimed is:
 1. A method of manufacturing an electrocatalyst,comprising: forming a metal layer on a substrate; treating a surface ofthe metal layer; and forming a catalyst layer on the surface-treatedmetal layer by applying potential to an aqueous deposition solutioncomprising a nickel precursor, a copper precursor, a phosphorusprecursor, and an additive, wherein a molar ratio of the nickelprecursor to the copper precursor is greater than about 49:1.
 2. Themethod of claim 1, wherein the metal layer comprises a nickel layer or acopper layer.
 3. The method of claim 1, wherein the treating the surfacecomprises treating the surface using a UV-ozone cleaning treatment. 4.The method of claim 1, wherein the potential is applied by a cyclicvoltammetry method.
 5. The method of claim 4, wherein a range of thepotential is of about −1.2 to 0.2 V.
 6. The method of claim 5, wherein afrequency at which the range of the potential is applied is of about 3to 15 times.
 7. The method of claim 1, wherein a molar concentration ofthe nickel precursor is of about 0.02 to 0.5 M.
 8. The method of claim1, wherein the nickel precursor comprises one or more of nickel sulfate,nickel nitrate, and nickel acetate.
 9. The method of claim 1, wherein amolar concentration of the copper precursor is of about 0.001 to 0.02 M.10. The method of claim 1, wherein the copper precursor comprises one ormore of copper sulfate, copper nitrate, copper acetate, and copperacetylacetonate.
 11. The method of claim 1, wherein the additivecomprises sodium acetate, and further comprises glycine or citric acid.12. The method of claim 11, wherein a molar ratio of the nickelprecursor to sodium acetate, glycine, or citric acid is about 1:about0.5 or greater and about 1:less than about
 2. 13. The method of claim11, wherein a molar concentration of each of sodium acetate, glycine,and citric acid is of about 0.05 or greater and less than about 0.2 M.14. The method of claim 1, wherein a molar ratio of the nickel precursorto the phosphorus precursor is of about 1:5 to 1:20.
 15. The method ofclaim 1, wherein a molar concentration of the phosphorus precursor is ofabout 0.1 to 1.25 M.
 16. The method of claim 1, wherein the phosphorusprecursor comprises sodium hypophosphite.
 17. The method of claim 1,wherein the substrate is pretreated using an oxygen plasma etchingprocess.
 18. An electrocatalyst comprising an oxygen generationelectrode and a hydrogen generation electrode, wherein at least one ofthe electrodes comprises a substrate and a catalyst layerelectrodeposited onto the substrate, and the catalyst layer comprisesgreater than about 65 at % of nickel; and less than about 35 at % ofcopper, based on 100 at % of metal atoms.
 19. The electrocatalyst ofclaim 18, further comprising a metal layer between the substrate and thecatalyst layer.
 20. The electrocatalyst of claim 19, wherein the metallayer comprises a nickel layer or a copper layer.
 21. A vehicle partcomprising an electrocatalyst of claim 19.